For more than a decade, our laboratory has been studying technology to develop, manage, and use formal descriptions of biomedical concepts. The result of this work is Protege-2000, a workbench that allows users to edit and apply controlled terminologies, ontologies, and knowledge bases to a wide range of information management problems. To date, more than 3500 people have registered as users of the system. Many diverse projects in biomedical informatics--including many supported by NIH--have become critically dependent on this software and the knowledge-engineering principles that it supports. This P41 application seeks to establish a biotechnology resource for the general support of Protege-2000 in a manner that will benefit the system's entire user community. We propose technology research and development to expand the capabilities of the Protege-2000 system to meet the current and anticipated needs of the user community. We will incorporate support for classification systems based on description logic within Protege-2000, allowing the system automatically to refine the relationships among concepts and to ensure that concepts are defined with adequate precision. We will develop new methods and tools to assist users in accessing libraries of predefined problem solvers (e.g., for heuristic classification, constraint satisfaction, plan generation) and in selecting and configuring those problem solvers to automate particular tasks. We also will continue to enhance Protege-2000 to accommodate the growing needs of our user community in building and managing large, heterogeneous, and distributed terminologies and knowledge bases. As a biotechnology resource, we will continue and expand our collaborative research projects with other Protege-2000 users. We will provide service to the Protege-2000 user community through enhanced technical support, user documentation, tutorials, and workshops. These activities will serve to disseminate information about the resource and will aid research and development in many aspects of biomedical informatics both in the United States and internationally.